Brushless direct current motors ensure that a rotational movement is maintained in that, after a specific angle of rotation has been covered, they ensure that the direction of current is reversed. This reversal of the direction of current is referred to as commutation. In order to be able to commutate at the right time, sensors, for example a Hall sensor, are provided in direct current motors and make it possible to evaluate the current angle of rotation. However, there are also variants which manage without sensors and, in this case, use the existing phases by means of skilled actuation to determine the current rotary position of the rotor in relation to the stationary stator by means of the electromotive force (EMF) produced by induction.
In the case of brushless direct current motors or synchronous motors, the rotor field and stator field must be adapted to one another, i.e. the fields must be synchronous and thus also change together with the speed.
Furthermore, it is possible to distinguish direct current machines comprising current reverser (commutators) and brushes from brushless direct current machines (brushless DC motor, BLDC) which are constructed in the manner of a three-phase synchronous machine. Three-phase synchronous machines can be excited electrically or by means of permanent magnets. In the case of electrically excited synchronous machines, the energy transmission into the rotor can also take place by means of slip rings and brushes.
Since the commutation point in time in the case of sensorless direct current motors takes place according to the induction and/or the EMF and/or the rotor angle, special effort is required to start up the motor from standstill, to slowly rotate it or to brake it.
The article ‘Position and Speed Control of Brushless DC Motors Using Sensorless Techniques and Application Trends’ by Jose Carlos Gamazo-Real et. al., 19 Jul. 2010, Department of Signal Theory, Communications and Telematic Engineering, University of Valladolid, from the journal sensors 2010, ISSN 1424-8220, deals with the position and speed control of brushless direct current motors.
The dissertation ‘Position-sensorless control for an accelerometer-supported, highly dynamic robot drive system with a permanently excited synchronous motor’ by Josef Reill, Dr. Hut Verlag, ISBN 978-3-86853-495-5, June 2010, in chapter 6 describes an EMF (electromotoric force) process which is used only above a minimum turning rate (number of revolutions) of the machine, at which rotational speed the induced voltage is present at a sufficient amplitude, and in chapter 7 describes a test signal process.
The article ‘Position Self-Sensing Evaluation of Novel CW-IPMSMs with an HF Injection Method’ by Xiaocan Wang et. al. in IEEE Transactions on Industry Applications, vol. 50, No. 5, September/October 2014 relates to a synchronous machine comprising permanent magnets which uses an HF injection process.
The document https://github.com/joewa/blde-strip/blob/master/README.md from July 2016 describes a project by Jorg Wangemann, Heiko Rothkranz et. al. for electronic speed control for a brushless DC motor (brushless DC, BLDC).
The article ‘Fault Tolerant Capability of Five Phase BLDC Motor with Ten Step Commutation’ by Cicily Antony T et. al. from the International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering, vol. 3, Special Issue 5, December 2014 describes a ten-step commutation logic for a BLDC motor which has five phases and a Hall sensor and compares the results with a four-phase and three-phase motor.
The document http://www.ti.com/lit/ml/sprt647/sprt647.pdf from the year 2013, USA, with document number SPRT647, describes the InstaSPIN™ FOC (field oriented control) control technology from Texas Instruments for synchronous (e.g. BLDC) or asynchronous (e.g. AC induction) motors which use the FAST™ (flux, angle, speed, torque) technology.
The article ‘A Comparison of Three Phase and Five Phase BLDC Motor’ by Kiran George et. al. from the International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering, vol. 2, Special Issue 1, December 2013, describes the ripple of a five-phase BLDC motor in comparison with a three-phase motor.
The article ‘Sensorless speed and position control of synchronous machines using alternating carrier injection’ by Ralph Kennel et. al. from the Electric Machines and Drives Conference, 2003, IEMDC'03, IEEE International, volume 2, p. 1211-1217, vol. 2, ISBN 0-7803-7817-2, 1 Jun. 2003, proposes a specific injection scheme using predefined injection angles.
The article ‘Sensorless Position Control of Permanent Magnet Synchronous Machines without Limitation at Zero Speed’ by Ralph Kennel et. al. from IECON 02 [Industrial Electronics Society, IEEE 2002 28th Annual Conference of the], volume 1, p. 674-679, vol. 1, ISBN 0-7803-7474-6, 5 Nov. 2002, describes a sensorless control algorithm for SMPMS machines (surface mounted permanent magnet synchronous machines) which uses a high-frequency voltage injection.
The article ‘Multilevel Multiphase Space Vector PWM Algorithm’ by Óscar López et al., IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 55, NO. 5, May 2008, pages 1933 to 1942 describes the use of more than three phases in drive devices, in particular an expression for calculating a duty cycle of a two-level converter.